A Light emitting diode (LED) is a solid-state semiconductor device, which directly transfers electricity into light. As a promising “Green Lighting Source” in the future, the white LED has such advantages as high luminous efficiency, power saving, non-thermal radiation and is free of heavy metals such as mercury, pollution and waste. The white light is produced through (i) blue light LED's stimulation of yellow phosphor; (ii) UV-light LED's stimulation of RGB three-wavelength phosphor; or (iii) RGB three-primary-color LED's blending of light. The first two methods, which produce light via LED's stimulation of phosphor, have the disadvantage of low light conversion efficiency, impure and uneven color since it is difficult to control phosphor coating during packaging; and the third method requires complex circuit driving and has high production cost, which is not suitable for commercial application.
The existing warm white LED comprises a base, a blue light wafer and a gold thread. The blue light wafer is fixed inside the base and the gold thread is fixed and connected with the blue light wafer and the base. A phosphor layer, a mixture of yellow phosphor and red phosphor, is coated over the blue light wafer surface. The base peripheral is packaged with epoxy glue. The blue light wafer's blue light stimulates the yellow light and red light from the phosphor and mix them into low-color-temperature warm white LED. The general luminous efficiency of this warm white LED is reduced by 40%-50% compared with conventional yellow phosphor as the white light is mixed with red phosphor which has low conversion efficiency.
Another warm white LED is coated with a yellow phosphor layer mixing blue light wafer and red light wafer on the outside surface to produce warm white light. However, in packaging, the light emitted by the red light wafer or the blue light wafer is easily absorbed by the other. For this reason, a certain distance is designed between the blue light wafer and the red light wafer, further resulting in blending of light; in addition, large packaging structure increases production cost; and blue light wafer and the red light wafer are independent and the complex bonding may lead to abnormality and high cost.